This application seeks support to study membrane transport in blood cells and tissue using electron probe microanalysis (EPMA). The electron probe is capable of elemental localization and quantitation on both cellular and subcellular levels. Transport problems which we plan to study utilizing established EPMA preparative techniques are: 1) heterogeneities in red cell transport, 2) role of hemoglobin in regulation of red cell volume, 3) sequence of membrane maturation and hemoglobin production in erythropoiesis, 4) transepithelial transport of calcium in rat kidney. A number of fundamental questions concerning transport in tissue have not been answered because of a lack of knowledge of cellular concentrations and distributions of various elements. EPMA can make this information available provided that additional preparative methods can be established which preserve cellular morphology and elemental distributions. A number of cryotechniques exist at present that are potentially capable of meeting these needs. We will evaluate these cryotechniques utilizing model systems in which EPMA and chemical analysis can be directly compared.